1. Field of the Invention
The present invention relates to a solid-state image sensor, and more particularly to a solid-state image sensor comprising photodiodes each of which has a micro-lens arranged thereover.
2. Description of the Background Art
Some conventional solid-state image sensors provide the wider dynamic range of an image signal representative of a scene captured while retaining, or without reducing, the photo-sensitivity of photodiodes or photosensitive cells. For example, in the solid-state image sensor disclosed in Japanese Patent Laid-Open Publication No. 298175/1992, hereinafter referred to as Document 1, two types of horizontal lines of photodiodes are arranged alternately in the vertical direction. Specifically, one type of horizontal line contains higher-sensitivity photodiodes and the other contains lower-sensitivity photodiodes. Then, every two photodiodes, vertically adjacent to each other, of different sensitivities work together as one pixel. Signal charges obtained from the two photodiodes separately from each other are added up to each other to form a signal charge of one pixel, which attains a wider dynamic range.
Where one pixel is composed of a couple of photodiodes of different sensitivities as disclosed in Document 1, problems such as lowering the sensitivity of the photosensitive cells and shading may likely occur depending upon, e.g. changing the exit pupil position of an imaging lens or the incidence angle of an imagewise light beam.
The problems are due to the lower-sensitivity photodiodes. Specifically, because of the lower-sensitivity photodiodes or the opening of the optical shielding film being smaller in area, a change of the exit pupil position or the incident angle may extremely reduce the amount of light incident on the lower-sensitivity photodiodes, thereby lowering the sensitivity of the photosensitive cells and causing shading.